1. Field of the Invention
This invention is directed to a plasma reactor, especially to a dry etching apparatus.
2. Description of the Background Art
FIG. 20 is a sectional view generally showing an ECR (electron cyclotron resonance) etching apparatus which is a kind of conventional plasma processing apparatus. In a plasma production chamber 1, plasma is produced from process gas by a xcexc wave 19 and transferred to a reaction chamber 2. The plasma exposes wafers 7 biased by an RF power obtained by an RF power supply means 8.
There are various parameters for controlling an etching process in the ECR etching apparatus, including shape and position of an ECR face 5 (which also depends on a magnetic field provided by coils 4), the RF power, the xcexc wave 19, a method of electrostatic chuck for the wafers 7, pressure from process gas or the like.
An apparatus of high integration and a fine structure has made it more and more difficult to achieve etching with high anisotropy, high selectivity and high uniformity. There are many cases that the present etching parameters are not enough to achieve a desirable etching. Anomalies in etching shape due to charge-up (referred to as xe2x80x9ccharge-up shape anomalyxe2x80x9d hereinafter) has been raised as one of problems to prevent the formation of a fine structure in recent years.
FIGS. 21 and 22 are enlarged sectional views in the vicinity of the surface of a semiconductor wafer 101, illustrating the charge-up shape anomaly. Each figure shows the behavior of ions (shown by circled xe2x80x9c+xe2x80x9d) and electrons (shown by circled xe2x80x9cxe2x88x92xe2x80x9d) when a fine pattern etching of the semiconductor wafer 101 is performed by means of a plasma etching.
In FIG. 21, an SiO2 film 13, an Si film 14 and a resist pattern 15 are formed one after another on the surface of the semiconductor wafer 101. The Si film 14 is etched with the resist pattern 15 as a mask. In this case, as etching proceeds, electrical neutrality is maintained by incidence of both ions and electrons on the surface of the resist pattern 15.
In a fine pattern 16, incidence of ions occurs perpendicular to the surface of the semiconductor wafer 101. Thus, ions can reach to a bottom surface 18 of the fine pattern 16 with no collision with side walls 17. On the other hand, electrons have no directional property to be incident on the side walls 17, thereby having difficulty in reaching to the bottom surface 18.
As shown in FIG. 21, when a conductive film such as the Si film 14 is etched, ions incident on the bottom surface 18 and electrons incident on the side walls 17 are recombined in the Si film 14 to be neutralized. Thus, electrical neutrality is maintained. On the other hand, when the bottom surface 18 moves downward due to the etching progress and exposes an insulating film such as the SiO2 film 13 as shown in FIG. 22, ions incident on the bottom surface 18 and electrons incident on the side walls 17 are not neutralized. Thus, the bottom surface 18 is positively charged up due to the ion incidence while the side walls 17 are negatively charged due to the electron incidence.
Therefore, the orbit of ions incident on the bottom surface 18 is bent by repulsion of positive charge on the bottom surface 18 and gravitation of negative charge on the side walls 17. This causes local incidence of ions on the interface between the Si film 14 and the SiO2 film 13, and then produces a V-shaped notch (reference character A shows notch amount).
To decrease such charge-up shape anomaly, a method for pulsing the xcexc wave 19 or the RF power (to repeat ON/OFF periods thereof) has been advocated. When both of the xcexc wave 19 and the RF power are in the ON period, normal discharge occurs, causing progress in charge-up in a fine pattern. On the contrary, when either of the xcexc wave 19 or the RF power is in the OFF period, incidence of electrons on the bottom surface 18 is made possible by no directional difference between ions and electrons, thereby dissolving charge-up. That is, charge-up proceeded during the ON period can be dissolved during the OFF period.
Such control over the movement of charged particles is very important not only for dissolution of shape anomalies but also for control of a selectivity ratio and uniformity. The method for pulsing conventional xcexc wave 19 and RF power is however limited, so that extension of pulse methods has been required for controlling broader etching parameters.
According to a first aspect of the present invention, a plasma reactor comprises a stage to which a frequency-modulated RF power is applied; and a reaction chamber containing plasma exposed to a sample mounted on the stage.
According to a second aspect of the present invention, a plasma reactor comprises a stage to which an RF power is applied; and a reaction chamber containing plasma exposed to a sample mounted on the stage, wherein the RF power fluctuates in cycles, each one of the cycles consisting of a plurality of first and second subcycles with the RF power of different amplitudes, wherein the plurality of first subcycles has different lengths, respectively.
According to a third aspect of the present invention, a plasma reactor comprises a stage to which an RF power is applied; and a reaction chamber containing plasma exposed to a sample mounted on the stage, wherein the RF power presents a waveform in which an AC waveform with a predetermined initial phase is intermittently superimposed on a DC value.
According to a fourth aspect of the present invention, an intermittently supplied xcexc wave produces the plasma.
According to the plasma reactor of the first aspect of the present invention, accumulation of charge occurring with the RF power of high frequency can be relieved with the RF power of low frequency. At the same time, deterioration in an etching rate, which is regarded as one of problems when only the RF power of low frequency is applied, can be relieved with the RF power of high frequency.
According to the plasma reactor in the second aspect of the present invention, in one cycle that the RF power fluctuates, the first subcycles have different lengths, respectively. Thus, charge-up can be relieved during one of the subcycles while deterioration in an etching rate can be suppressed during the other of the subcycles.
According to the plasma reactor in the third aspect of the present invention, an area more positive than DC components becomes larger than that more negative than DC components in the range of superimposition of RF components by setting the initial phase within the range of 180xc2x0 to 360xc2x0. This results in improvement in a notch amount and a selectivity ratio. Further, the area more positive than DC components becomes smaller than that more negative than DC components in the range of superimposition of RF components by setting the initial phase within the range of 0xc2x0 to 180xc2x0. This results in improvement in a CD gain and an etching rate.
According to the fourth aspect of the present invention, an intermittent introduction of the xcexc wave into the plasma reactor leads to reduction in a notch amount. Further, an intermittent application of the RF power to the stage leads to a remarkable effect in improving etching characteristics.
The object of this invention is to provide a plasma reactor capable of extending etching parameters for reducing charge-up shape anomaly in dry etching and for improving etching performance such as selectivity, uniformity and workability.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.